Interconversion of mechanical and chemical energy lies at the core of nearly all adaptive responses exhibited by living systems. From the simplest bacteria to complex mammals, survival is dependent upon the organism's ability to extract meaningful signals from the environment and to respond via sophisticated mechanochemical receptors and chemical signaling. Our hearing ability via mechanosensory hair cells and the neural system, the muscle contraction via ATP-regulated power strokes of myosin motors, and the rotary motion of flagella using molecular motors in the cell are examples of such interconversion.
The concept of a system, which converts chemical energy to mechanical energy and vice versa, is of basic interest; but of further consequence is a system which connects two chemistries with an intermediate mechanical step: a chemo-mechano-chemical or C-M-C system, as in the case of ATP synthase. Importantly, what distinctly sets biological mechanochemical systems apart from artificial materials systems such as sensors and actuators is their ability to self-regulate via cyclic energy flow within feedback loops; a mechanical stimulus generates a chemical signal that in turn drives another mechanical response, etc. The human body utilizes feedback mechanisms to promote homeostasis and maintain its core temperature, blood, pH, and sugar/glucose levels, all facilitated by information exchange between blood vessel or organs as a receptor, brain as a control center, and muscles, insulin or other components as effectors. For example, the human body also has a remarkable capacity for precisely regulating its core temperature within less than 1° C. by utilizing feedback mechanisms, which include sensing and actuating, e.g. shivering, vasoconstriction, neurotransmitter secretion, perspiration, etc. to achieve homeostasis. Indeed, the entire Earth functions as a vast homeostatic superorganism comprised of countless feedback loops involving everything from climate conditions to adaptation/extinction of species over time.
In synthetic systems, chemical-mechanical transduction has been approached from two separate angles: chemo-mechanical (C→M) and mechano-chemical (M→C) pathways. Examples include the nanomechanical biomolecular detector, responsive polymer-based actuators and synthetic molecular transporters as C→M devices, and damage sensors and shear-induced optics as M→C devices; no such synthetic systems provide for a feedback mechanisms that involve both C→M and M→C modes to lead to a self-regulated C→M→C transduction, which is fundamental to regulatory functions that would allow the system to self-regulate and autonomously control its state (temperature, pH, pressure, metabolite levels, etc.)
The development of sensitive and high-throughput biomolecule separation assays capable of rapid non-destructive sorting is crucial for advancing both medical diagnostics and biological discovery, such as cell counting, sorting, biomarker detection and protein engineering. Traditional protein separation and purification techniques include affinity chromatography, size exclusion, ion-exchange, and counter-current chromatography, often performed with a fast-performance liquid chromatograph (FPLC). These methods work with large amounts of target material (μg-mg) and typically require modification of the target proteins with an affinity tag (ie. His, FLAG) or several rounds of purification, sometimes lasting several days. However, to perform rapid tests with sub-microliter sample volumes, miniaturized devices with comparable or higher efficiency would be desirable. While significant progress has been made on microdevices for either separation or detection, current devices have the following limitations: 1) the target molecules need to be modified with handles such as fluorophores or streptavidin, which can change the native functions of the protein and preclude analysis of unmodified samples; 2) the detection and separation methods require the use of electric fields, IR, or magnetic fields; 3) the release of the target molecules necessitates destructive strategies such that the separation device can only be effectively used once (or a limited number of times); and 4) in some cases, biomolecules of similar sizes or similar chemical nature (including charge, conformation, hydrophobicity, etc.) are not able to be well-discriminated. Recently reported devices configured for gentle capture-and-release require washing and elution steps to separate targets from non-targets; however, devices that perform concerted capture, separation, and release which do not need extensive washing and elution are not available. As a result, cost-efficient, easy-to-implement microdevices capable of catching unmodified biomolecules and releasing them in a way that retains native function are highly desired and would allow collection of target molecules for downstream quantitative analysis or further use.